The present invention relates to a rudder with wings for facilitation of energy saving and a method for manufacture thereof.
In order to increase the steering efficiency of the rudder of a ship, it is advantageous to locate the rudder in the fast propeller slip stream. Therefore the rudders are normally located behind the propeller. In addition to steering the ship, the rudder has a function of propelling the ship. That is, when the rudder encounters the propeller slip stream, the lift is developed so that the propulsion component of the lift serves to propel the ship.
The mechanism of a conventional symmetrical-airfoil shaped rudder for developing the propulsion force will be described.
FIG. 1 shows a view of a propeller 1 from the stern of a ship. In general, the propeller 1 is rotated in the clockwise direction i so that the helical propeller slip stream including rotating streams a-h is formed. FIG. 2 shows a rudder 2 located in the propeller slip stream so that as shown in FIG. 3 oblique streams 3 and 4 impinge against the rudder 2.
In FIG. 3, V.sub.U is a vector indicating the stream flowing upwardly from the axis j of the propeller; V.sub.L is a vector indicating the stream flowing downwardly; L.sub.U is a lift developed by the flow V.sub.U ; L.sub.L is a lift developed by the flow V.sub.L ; T is a thrust; .theta..sub.U indicates the direction in which the lift L.sub.U acts; and .theta..sub.L indicates the direction in which the lift L.sub.L acts. When the rudder angle is 0.degree. as shown in FIG. 3, the thrust T=L.sub.U cos.theta..sub.U +L.sub.L cos.theta..sub.L is produced. That is, the rudder 2 converts part of the energy of the propeller slip stream into the propulsion force. In other words, the rudder 2 functions as a propulsion device.
However, the energy of the propeller slip stream cannot be satisfactorily recovered when only one rudder blade is located vertically in the propeller slip stream. That is, only the streams d, e and h, a as shown in FIGS. 1 and 2 are utilized.
One of the object of the present invention is therefore to provide a rudder which effectively converts the energy of the propeller slip stream into the propulsion energy.
Another object of the present invention is to provide a method for manufacturing the rudder of the type described in a simple manner yet with a high degree of accuracy.
Preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.